Method and furnace apparatus for calcining carbonate material and for other purposes



June 3, 1947.

GE. CONNOLLY METHOD AND FURNACE APPARATUS FOR CALCINING CARBONATEMATERIAL AND FOR OTHER PURPOSES Filed April 21. 1943 2 Sheets-Sheet 1 INVE N TOR GEOEG'EE. CONNOLLK y. ATTORNEYS June 3, 1947. E. CONNOLLY2.421.542 v uz'r AND I NA APPARATUS FOR cnmm on ATE MATERI AND FORo-runn nrosss Filed April 21, 1943 2 Sheets-Sheet 2 nvmvrox GEORGEECONNOLLL ATTORNEYS Patented June 3, 1 947 ME' I'HOD AND FURNACEAPPARATUS FOR CALCINING CARBONATE MATERIAL AND FOR OTHER PURPOSES GeorgeE. Connolly, San Francisco, Calif., assignor to Nichols Engineering &Research Corporation, a. corporation of Delaware I Application April 21,1943, Serial No. 483,920

9 Claims. (Cl. 263-26) This invention relates to furnace apparatus andmethods adapted, among other uses, for calcining carbonate materials andfor the simultaneous recovery of oxide products and gases having a highcarbon dioxide content.

In accordance .with the present invention, materials such as limestonefines and magnesite fines may be calcined in a multiple hearth furnaceof the well-known so-called Herreshoif class. While it has heretoforebeen proposed to calcine limestone and the like in furnaces of thisclass, it has generally been found difficult or impossible to do soeconomically while at the same time obtaining a carbon dioxide gasproduct of high concentration and free to a desired extent from gaseousproducts of fuel combustion. 'That is, in order to economically heatthefurnace to the necessary high temperatures for such a process, it hasbeen considered neces'sary to burn fuel in the presence of the materialbeing calcined, and this in turn inherently involves, dilution of thecarbon dioxide product with gaseous products of fuel combustionand air,in excessive amounts difficult to control or regulate. It is possible toapply muffle heating by known methods to furnaces of this class, tothereby avoid burning the fuel in the presence of the material undertreatment, and it is contemplated that various fea-' tures of thepresent invention may be utilized with muille heating of the furnace.However, mufile heating arrangements are generally relativelyinefiicient andthe passages and cavities of the mutlle heaters are.diflicult to keep clean for proper heat transfer, and free from beingblocked by dust and soot. Consideration has also been given to heatingfurnaces of this class electrically in cases where burning of fuel inthe presence of the material being calcined is undesirable. But so faras is known, no method or apparatus has heretofore been available forelectrically heating furnaces of this class in a dependable andeconomical way and with which the resistors will withstand therelatively high temperatures necessary for calcining carbonates, orcomparable uses.

In accordance with the preferred form of the present invention,provision is made for dividing the multiple hearth furnace into threezones which are preferably separated against free passage of gasesbetween adjacent zones, the first zone being adapted for drying andpreheating, the second zone being heated by a novel arrangement ofelectrical resistance units so that the burning of fuel in this zone isavoided, and whereby the greater part of the carbon dioxide gasavailable ered from this zone, largely or wholly free of air orcombustion gases. The third zone provides a chamber or chambers withinwhich the material under treatment may be further dissociated to thedesired extent and preferably by higher temperatures. This latter zonemay be economically heated by the combustion of fuel therein and theresulting gaseous products may be conveyed into the first zone toprovide heat for the drying and preheating purposes. With thisarrangement the relatively expensive electrical heating may beeconomically confined to the second zone which is preferably heated onlyto a moderately high temperature which the resistors will safelywithstand, and from which the gases of high carbon dioxide content arerecovered, whereas the heat for drying, preheating and also for thefinal thorough high temperature calcining, may be supplied at lessexpense by the burning of fuel.

The invention further embodies novel features of construction andarrangement of the electrical heating means and novel features of thefurnace construction, particularly adapted among other uses, forcarrying out the above indicated method.

Various further and more specific objects, features and advantages willmore clearly appear from the detailed description given below taken inconnection with the accompanying drawings which form a part of thisspecification and illustrate merely by way of example, a preferred formof the invention. The invention consists in such novel features,arrangements and combinations of parts as may be shown and described inconnection with the apparatus herein disclosed and also such novelmethods as are disclosed and described hereinafter.

In the drawings:

Fig. 1 is a vertical sectional view of a. multiple hearth furnaceconstructed in accordance with the invention;

Fig. 2 is a horizontal sectional view taken substantially along line 2-2of Fig. 1;

Fig. 3 is an enlarged vertical sectional view taken substantially alongline 3-3 of Fig. 2;

Fig. 4 is an enlarged view showing one of the electrical heating unitsand its mounting;

Fig. 5 is a horizontal sectional view taken substantially along line 5-5of Fig. 1 and showing novel features of internal construction of a shaftsection of the rabbling structure; and

Fig. 6 is a vertical sectional view of the structure of Fig. 5.

As shown in Fig. 1, the furnace may comprise 3 a cylindrical wall Inembraced by an outer metal shell as at H. The furnace may be providedwith a plurality of superposed hearths as at 12-22 inclusive, eachaccompanied by two or more rabble arms as at 23 carried by a centralvertical shaft 24 adapted to be rotated through gearing as at 25connected to a suitable source of power. The even numbered hearths maybe formed with peripheral ports or openingsflas at 26, the interveningodd numbered hearths being formed with central ports or drop openings asat 21, whereby as the rabbling structure is rotated, rabble teeth as at28 act to periodically agitate and gradually advance the material beingtreated over each hearth and from hearth to hearth down through thefurnace, the material being passed outwardly and inwardly respectivelyon alternate hearths. The upper hearth l2 or furnace top which may serveas a preliminary dryin hearth may have its port or ports fitted withsome well-known type of feeding device as schematically indicated at 29.Gases may be withdrawn from within the upper part of the furnace throughan outlet flue 30, and the treated calcines may be discharged from thebottom of the furnace through any suitable known type of outletconstruction as at 3|. The features of construction as thus fardescribed in this paragraph, are in accordance with wellknown types ofHerreshoff furnaces, one example of which is disclosed in further detailin U. S.

patent to Baird 1,669,925, granted May 15, 1928, reference to which maybe had as to further details of construction.

While in the most common furnaces of this type the gases are free totravel countercurrent to the material being treated, from the lowerhearths up through the various hearth ports and out from the top of thefurnace, on the other hand, with the preferred embodiment of the presentinvention, the hearths are divided into groups to form three zones, thatis, an upper zone located within the furnace between hearths l2 and I6for example, an intermediate or middle zone located between hearths l 6and for example, and a lower zone between hearths 20 and 22. The upperand middle zones, and similarly the middle and lower zones, may beisolated against the direct or free passage of gases from one zone tothe next, by so-called ore luted feed devices as at 32, 33 of a suitableknown type. These devices may'comprise for example a shelf or plate 34mounted beneath the hearth port so that suificient material will falland accumulate on the plate to normally keep the port closed againstfree passage of gas. The rabble arms at this region may be provided withfeeding arms or scoop members as at 35 so that each time the rabble armpasses the plate 34, a predetermined amount of the material will bedislodged from the plate and fed to the hearth below. The furnace isthus effectively divided into an upper drying and preheating zone, anintermediate calcining zone, and a lower zone for completion of thecalcining.

The lower zone may be heated by the combustion of fuel therein, forexample by the use of oil burners as at 36. The resulting gases in thiszone may be conducted from the upper part of this zone, for example froma point just beneath hearth 20, by a conduit 31 extending up into theupper zone preferably to the lower part of the upper zone, or at a pointjust under hearth No. 15. Thus the hot gaseous products of combustion ofthe fuel in the lower zone, together with some air and gases dissociatedfrom the material under final treatment, are carried up 4 to the dryingand preheating zone to normally supply sufllcient heat to the upperzone. If desired, additional heat may be obtained by burning fuel in theupper zone, as by the use of one or more oil burners such as indicatedat 38.

, As shown, the hearth spaces in the middle zone may be heated withoutcombustion of fuel in this zone by the use of electrical resistanceheating units indicated at and hereinafter more fully described inconnection with Figs. 2-4.

It is intended to carry on the calcining process in the furnacecontinuously and since the intermediate zoneas thus far described may besubstantially sealed against the entrance of air or gases of combustion,once the process is well under way, the atmosphere in the middle zonewill comprise solely the gases evolved from the material undertreatment. These may be withdrawn through an outlet conduit as at 4|.

In cases where it is unnecessary that the gases from outlet 4| entirelycomprise gas evolved from the material under treatment, it may bedesirable to introduce into the middle zone some of the gas drawn oil.from the lower zone. This may be done by using a conduit 42 branchingoff from conduit 31 and entering the middle zone preferably at its lowerpart, for example just below hearth I9. The amount of this gas may bevaried or regulated as by a damper 43 in conduit 42. In cases where acertain amount of combustion gases and/or air is not objectionable inthe middle zone, the middle zone ma generally be heated with lessexpense by thus supplementing the electrical heaters with apredetermined controlled or regulated amount of the gases from the lowerZ0116.

A present preferred construction and arrangement of the electricalheating units for the middie zone is shown in Figs. 2-4. These units maycomprise for example non-metallic ceramic rods as at 40, of siliconcarbide material, one form of which is now commercially available underthe name Globar. As best shown in Fig. 2, these rods may be placed in apolygonal arrangement, for example a hexagonal pattern as shown, aroundthe inside walls of each hearth space. As shown 3, several of the rods,for example four, may be mounted in superposed positions at each side ofthe polygon, The ends of each resistance rod or unit may be slidablymounted in insulation bushing members as at 46. The interior wallsurfaces of the furnace may be suitably formed or cut away as at 41 toafford space between the rods and the wall surfaces. The heating unitsmay thus be largely inset with respect to the normal interior contourline of the furnace wall so that the operation of the rabble arms is notinterfered with and also the material under treatment is free to fallthrough the hearth ports 26 without falling on the heating elements.

Heating units of the above mentioned type are ordinarily formed with ahigh resistance central portion and low resistance ends so that the endportions will be at a relatively lower temperature and thus not injurethe mounting means. The exterior wall surface of the furnace may beformed at circumferentially spaced points with cavities as at 48 linedif desired with suitable heat-resistant metal pieces as at 49 forstrengthening and protecting these portions of the walls and providingspaces for mounting and for ready access to the electrical terminals 50of the heating units. It' will be further noted that the cavities 48 andthe lining members 49 therefor are al- I so so shaped that any of theresistance units may be withdrawn or reinserted by sliding the samelongitudinally through their insulation bushings l8. 1

The terminals 50 may be of a suitable known type readily removable topermit the insertion or replacement of the resistance units to whichthey are connected. As will readily be understood, the variouselectricalresistance units shown may all be connected in parallel to a source ofpower or in various known series-parallel arrangements if desired,depending upon the voltages available *by heating the latter zone to asomewhat higher and the resistance values of the particular units 1 1,.1mm. Thefpolyg' onal arrangement -oi! the heating units has a number ofimportant advantages. In

case the material being treated, as is usual, has a tendency to causeconsiderable dust to arise within the furnace, quantities of such dustwill tend to accumulate on the resistance rods, and thereby seriouslyimpair the heating efficiency. It is therefore desirable to provide anarrangement whereby such dust may be frequently and quicklyremoved fromthe heating units without interrupting the operation of the furnace.This may be easily accomplished with the above de-' scribed constructionmerely by electrically disconnecting and sliding out each unit so thatthe dust is scraped off as the unit slides through one of its insulationsupporting bushings 46. The polygonal pattern of the units extendinghorizontally along the inside walls of the furnace further provides aconvenient arrangement whereby the electrical terminals and connectionsmay all be located entirely outside the furnace and thus free fromoverheating and in a position where they can be quickly and easilydisconnected whenever it is desired to inspect, clean,

repair or replace any unit while the furnace is in direct firing. Inlocations where electric power is inexpensive, the same arrangement ofheating units may of course be extended to other hearths in addition tothe middle zone of the furnace.

Where the method and apparatus are used for site, sufllcient fuel may beburned in the lower calcining materials such as limestone or magnezone,supplemented by such fuel, if any, as is necessary in the upp r zone, sothat the temperature of the calcines upon passing into the middle zonemay, for example, be in the neighborhood of 1000 F. At this temperaturelittle or no carbon dioxide will be given off. Then in the middle zone,sufficient electrical heating may preferably be provided to heat thecalcines to a temperature for example of 1600 F. before same pass to thelower zone. This temperature and the normaltime of treatment in themiddle zone (from twenty to sixty minutes) will be-suiiicient 70 tocause the greater part of the carbon dioxide gas to be evolved from thematerial, but normally insufficient to completely dissociate thecarbonate in this zone. The dissociation may be temperature, for exampleseveral hundreds of degrees higher. 7

The most desirable temperatures in the middle and lower zones willdepend upon the relative Eases, the damper 43 may be opened somewhat orregulated so that some hot gases from the lower zone will pass throughconduit 42 and contribute to the heating of the middle zone and thussupplement the generally more expensive electrical heating, withinlimits permissible by the character of gas desired from the middle zone.When the damper 43 is kept closed, the gases passing out through conduitII from the middle zone will consist almost entirely of carbon dioxidewhere the material under treatment comprises limestone or magnesite. Thegases passing out through flue 30 will be relatively low in carbondioxide.

The division of the furnace into three 'zones arranged as abovedescribed, makes possible the use of fuel for the preliminary dryingand'preheating and final calcining operations, thus conflning thegenerally more expensive electrical heating to the middle zone. Also theperformance of the calcining steps in two successive zones, permits themiddle or electrically heated zone to be operated at a temperaturesomewhat lower than that required for thorough calcining in the lowerzone. This permits the electrical heaters to be operated at temperatureswhich-will not be unduly destructive of the unit, yet high enough topermit recovery from the middle zone of the greater part of theavailable carbon dioxide, while confining the higher temperaturesnecessary for thorough dissociation to the lower zones having noelectrical heaters subject to being burned out.

The exclusion of gases of fuel combustion from the middle or maincalcining zone also has the advantage of greatly reducing the gas volumecarried out of this zone. This in turn reduces the amount of sensibleheat loss from the furnace in this gas, because of the less weight ofsuch gas. Also the reduced gas volume exited from the middle zonereduces the dust loss from this zone, because of the lowervelocity ofthe small quantity of gas.

While in the example shown, the furnace is provied with 10 hearths inaddition to the top drying hearths, it will be understood that theprinciples of the invention are applicable to furnaces having a greateror lesser number of hearths in each zone.

In view of the high temperatures at which the furnace is operated, it ispractically necessary to provide internal cooling air conduits withinthe rabbllng structure. As in the types of Herreshoif furnacesheretofore available, cooling air may be introduced through a conduit 5iconnected by suitable known means to the base of the central shaft. Asshown in Fig. 5, the shaft 24 may be double walled, i. e., with an innershaft 52 comprising a, cooling fluid conduit and with a space 53 betweenthe inner and outer walls providing a return path to the top of theshaft, for the cooling fluid after it has been conducted into and out ofthe various rabble arms. The above completed to the extent desired inthe lower zone mentioned Baird patent discloses one suitable eitherextended radially, or tangentiallyto both sides of each rabble armsocket in the inner shaft as shown in-Fig. 11 of the above mentionedBaird patent. However, if the furnace temperatures are subject to widevariations or are quite high, as necessary in the lower zone as operatedin accordance with this invention, there will be substantial danger thatthe expansion or contraction of the shaft sections due to temperaturechanges or diiferences, will cause such ribs or webs as heretofore used,to crack. That is, the inner and outer walls of each shaft section beingrigidly held in place by the integralribs or webs,

will not be sufficiently free to move in any direc-.

tion enough to accommodate the expansion or contraction of the parts,particularly if blasts of cool air should be introduced at any time intothe central cavity, or where the incoming cooling air is of a necessarylow temperature to adequately cool the rabble structure at hightemperature hearths such as involved with the present invention. And ifthese ribs or webs become cracked, the rabble arm sockets in the innerconduit 52 will be ineffective for securely retaining the rabble arms inposition when the rabbling force is applied thereto, as the innerconduit 52 may become more or less free to move out of place or alsobecome cracked, or open up at the joints between adjacent sections.

To eliminate these difficulties, I have devised an improved arrangementof these webs or ribs as shown in Figs. 5 and 6. That is, a plurality ofthe ribs are provided as at 5 extending substantially along successivetangents to the inner wall, and all in the same direction, to the rightor left, from the points of tangency adjacent each arm socket, wherebyupon expansion or contraction of the webs, or upon relative changes ofdiameter of the inner and outer walls, all of the webs will cooperate intending to rotate the inner wall slightly with respect to the outerwall,

in the same direction, clockwise or counterclockwise. This slightrelative'rotation of the inner wall with respect to the outer wall, thusrelieves the stresses which occur due to expansion or contraction of thevarious parts of the structure upon temperature changes. As a result,the tendency of the ribs to crack is eliminated. Yet it is stillpossible to cast the inner and outer walls and ribs of each shaftsection integrally, and rigidly to the extent necessary for propersupport of the rabble arm sockets.

In some cases further difficulties will 'occur due to uneven expansionand contraction of the inner and outer walls of the shaft sections. Forexample, if the socket regions at the upper part of the shaft section ofFig. 6 should become heated much more than the lower part of thissection, then there will be a tendency for the inner wall of the sectionto be twisted and become cracked, or the excessive axial expansion ofthe upper portion of the inner wall of the section may-set up axialstresses, tending to crack the integral ribs 54. To eliminate thesedifficulties, the inner wall of the section may be severed 8 as at 55 ata region intermediate the elevations of the two sets of sockets. Thesevered ends of the inner conduit may be formed with flanges as at 56and so made as to be adapted to receive a ring member 51, which providesa slidable and rotatable joint. This joint thus permits the upper andlower portions of the inner conduit to relatively rotate as well as toalso move axially with respect to each other, to the extent necessary torelieve the stresses. The ring 56 may for example comprise a split sheetmetal ring adapted to be inserted to spring into place after theremainder of the casting has been completed.

While the invention has been described in detail with respect to aparticular preferred example, it will be understood by those skilled inthe art after understanding the invention that various changes andmodifications may be made without departing from the spirit and scope ofthe invention, and it is intended therefore in the appended claims tocover all such changes and modifications.

What is claimed as new and desired to be secured by Letters Patent is:

1. Method for calcining carbonate material for the recovery of oxide andgas of high carbon dioxide content, comprising passing the materialsuccessively over a plurality of superposed hearths, including an upperhearth or hearths forming a drying and preheating zone, an enclosedplurality of hearths forming an intermediate zone and another enclosedhearth or hearths forming a lower zone, subjecting the material in saidlower zone to a time and temperature treatment in the presence ofburning fuel, suflicient to largely complete dissociation of thecarbonate, conducting resulting hot gases from said lower zone into theupper zone to heat the latter, subjecting the material in theintermediate zone to a time and temperature treatment suificient todissociate the carbonate therein to a substantial extent while largelyor wholly excluding gases of combustion therefrom, and withdrawing theresulting gas of high carbon dioxide content from said intermediate zoneindependently of the gases passed from the lower zone into the upperzone.

2. Method for calcining carbonate material for the recovery of oxide andgas of high carbon dioxide content, comprising passin the materialsuccessively over a plurality of superposed hearths, including an upperhearth or hearths forming a drying and preheating zone, an enclosedplurality of hearths forming an intermediate zone and another enclosedhearth or hearths forming a, lower zone, maintaining separation betweensaid zones against free passage of gases between adjacent zones,subjecting the material in the intermediate zone to a time andtemperature treatment suflicient to dissociate the carbonate therein toa substantial extent, by introducing heat into such zone electrically,subjecting the material in said lower zone to a time and temperaturetreatment in the presence of -'b fuel, to further dissociate thematerial, conducting resulting hot gases from said lower zone into theupper zone to heat the latter, and withdrawing the resulting gas of highcarbon dioxide content from said intermediate zone independently of thegases passed from the lower zone into the upper zone.

3. Method for calcining carbonate material for the recovery of oxide andgas of high carbon dioxide content, comprising passing the materialsuccessively over a plurality of superposed hearths, including an upperhearth or hearths forming a drying and preheating zone, an enclosedplurality of hearths forming an intermediate zone ment in the presenceof burning fuel, to furtherdissociate the material, conducting resultinghot gases from said lower zone into the upper zone to heat the latter,also conducting a controlled portion of said hot gases from said lowerzone into the intermediate zone, and withdrawing resulting gas of highcarbon dioxide content from said intermediate zone independently of thepart, of

the gases passed from the lower zone into the upper zone.

4. A furnace for calcining carbonate material for the recovery of oxideand gas of high carbon dioxide content, comprising a plurality ofsuperposed hearths, rabbling structure for advancing the material overeach hearth and from hearth to hearth down through the furnace, saidhearths including an upper hearth or hearths forming a drying andpreheating zone, another plurality of hearths forming an intermediatezone, another hearth or hearths formin a lower zone, means separatingsaid zones against free passage of gases between adjacent zones, meansfor heating the intermediate zone without combustion of fuel therein toa temperature sumcient to dissociate the carbonate therein to asubstantial extent, means for burning fuel in said lower zone t heatsame to a temperature sufficient to cause further dissociation of thecarbonate therein, means for conducting the gases resulting in saidlower zone into the upper zone for heating the latter, and outlet meansfor conducting away the gas of high carbon dioxide content formed insaid intermediate zone, independently of'the gases conducted into theupper zone from the lower zone.

5. A furnace for calcining carbonate material for the recovery of oxideand gas of high carbon dioxide content, comprising a plurality ofsuper-- posed hearths, rabbling structure for advancing the materialover each hearth and from hearth to hearth down through the furnace,said hearths including an upper hearth or hearths forming a drying andpreheating zone, another plurality of hearths forming an intermediatezone, another hearth or hearths forming a, lower zone, means separatingsaid zones against free passage of gases between adjacent zones, meansfor burning fuel in said lower zone to heat same for final dissociationtreatment of the material, means for conducting the resulting gases fromsaid lower zone into the upper zone for heating the latter, electricalresistance means within the intermediate zone for heating same withoutcombustion of fuel therein, to a temperature sufficient to dissociatethe carbonate therein to a substantial extent, and outlet means forconducting away the gas of high carbon dioxide content formed in saidintermediate zone.

6. A furnace for calcining material subject to dissociation by heat toform a gaseous product and a solid product, comprising a plurality ofsuperposed hearths, rabbling structure for advancing the material overeach hearth and from hearth to hearth down through the furnace, saidhearths including an upper hearth or hearths forming a drying andpreheating zone, another 10 plurality of hearths zone, another hearth orhearths forming a lower zone, means separating said zones against freepassage of gases between adjacent zones, means for heating theintermediate zone without combustion of fuel therein to a temperaturesufilcient to dissociate the material therein to a substantial extent,means for burning fuel in said lower zone to heat same to a temperaturesufficient to cause further dissociation of the material therein, meansfor conducting the resulting gases from said lower zone into the upperzone for heating the latter, and outlet means for conducting away thesaid gaseous product formed in said intermediate zone, independently ofthe gases conducted into the upper zone from the lower zone.

'7. Method for continuously calcining supplies of carbonate material forthe recovery of oxide and gas of high carbon dioxide content,comprising, drying and preheating the material by applying theretogaseous products of fuel combus tion, introducing the resulting hotmaterial into a chamber heated electrically to a temperature sufficientto cause dissociation of the material to a substantial extent,withdrawing from said chamher the carbon dioxide gas as formed therein,transferring the material from said chamber while hot to anotherchamber, applying heat by burning fuel in the latter chamber, to causefurther dissociation, and utilizing gases resulting in the latterchamber as a supply of said gaseous products of fuel combustion for saiddrying and. preheating step. t

8. In a furnace construction comprising a plurality of superposedhearths and rabbling arms carrying teeth for advancing material oversaid hearths and from hearth to hearth down through the furnace, acentral rotatable vertical shaft for carrying said arms, said shaftbeingformed of double walled sections providing an inner cooling fluidconduit surrounded by another fluid cavity between the inner and outerwalls, said walls respectively being formed with aligned sockets forreceiving each of said arms, a plurality of said sockets being providedat each of two elevations in each of said shaft sections, the inner wallof each section being formed with a slidable and rotatable joint at aregion intermediate said two elevations, and a plurality of rib means atboth the upper and lower regions in each section integrally formed withboth the inner and outer walls and extending from the inner wall to theouter wall substantially along successive tangents to the inner wall,and all in the same direction, to the left or right, from the points oftangency, whereby upon expansion or contraction of the webs, all willcooperate in tending to rotate the inner wall slightly with respect tothe outer wall, in the same direction, clockwise or counterclockwise.

9. In a furnace construction, rotary rabble arm supporting meanscomprising a central rotatable vertical shaft, said shaft being formedof double walled sections providing an inner fluid conduit surrounded byanother fluid cavity between the forming an intermediate 11 limitedrelative vertical and rotational move- Nu b ment. 1,549,379 GEORGE E.CONNOLLY. 1,861,213 1,678,875 REFERENCES CITED 2,225,199 The followingreferences are of record in the $263,464 file of this patent: UNITEDSTATES PATENTS 1:088:496 Number Name Date 10 4 1,912,811 Wechter June 6,1933 Name Date Pike Aug. 11, 1925 Greene May 31, 1932 Rohn July 31, 1928Abbott Dec. 17, 1940 Seipel Dec. 30, 1941 Paitrowitz Apr. 8, 1930 BairdMay 15, 1928 Wedge Feb. 24, 1914 Wedge Feb. 10, 1914

